The use of electric trolling motors on fishing boats has grown dramatically in recent years. It is now commonplace to use two propulsion means--a gasoline outboard to get to and from the fishing site and a much quieter electric trolling motor for maneuvering at the site, resisting current, or trolling.
In many cases, the electric trolling motor is suspended from a mounting structure which is attached to the boat near its bow, usually on a small forward deck surface. Whatever the nature of the mounting equipment, the electric motor is normally suspended in its operative position at the bottom of a vertical tube structure held just beyond the edge of the boat. The tube structure usually has an outer tube which is gripped nonrotatably by a portion of the mounting bracket, and a rotatable tube inside the outer tube which may be turned within the outer tube to set the direction of the motor attached at the bottom end thereof.
Since the electric motor is suspended underwater, it often strikes submerged objects, such as rocks. Such collisions may be quite damaging to the motor and to the mounting structure.
A variety of devices have been developed to absorb the shock of underwater collisions involving submerged motors and portions thereof. The prior United States patents include U.S. Pat. Nos.: 1,460,570; 1,523,909; 1,559,616; 1,780,552; 1,890,938; 1,990,387; 2,713,842; 2,957,441; 2,972,977; 3,003,724; 3,075,490; 3,246,915; 3,347,540; 3,460,506; 3,470,844; 3,698,673; 3,915,417; 3,948,472; 4,009,900; and 4,033,530.
The shock-absorbing devices of the prior art have a number of drawbacks and deficiencies. For example, the device disclosed in U.S. Pat. No. 3,915,417 allows pivoting movement of an electric trolling motor striking a submerged object when the boat is moving forward, but not when the boat is moving backwards. A spring device mounted in a substantially horizontal member of such device is extensible, but not compressible.
The devices disclosed in U.S. Pat. Nos. 3,470,844 and 1,523,909 each have two horizontal springs which absorb some shock, but fail to provide shock absorbing in several directions. In some cases, connecting devices limit the degrees of freedom of some shock-absorbers and limit their potential usefulness with electric trolling motors.
U.S. Pat. No. 1,780,552 discloses a two-by-two array of vertically disposed springs. While such a device allows a motor to rise over a submerged object exerting force against the bottom of the motor, little or no shock-absorbing movement in a horizontal direction, as is more typically needed, would be provided. Indeed, the springs would not ever undergo compression when an object is struck.
In short, there has been a need for an improved shock-absorbing mount for an electric trolling motor. A mount capable of absorbing shock which is taken through the vertical shaft structure in various directions is needed.